Electrically heated jet propulsion unit



6 0 2 5 3 v 555mm mm 1959 A. E. c. DENOVAN ETAL 2,918,004

ELECTRICALLY HEATED JET PROPULSION UNIT Filed Oct. 20, 1953 z/vvEA/ToRs United States Patent ELECTRICALLY HEATED JET PROPULSION UNIT Alexander Ewing Crawford Den'ovan, Stanmore, Dennis James Hodgson, Oxhey, and Henry Kremer, Highgate, London, England Application October 20, 1953, Serial No. 387,091

Claims priority, application Great Britain October 21, 1952 5 Claims. (Cl. 102'49) This invention is for improvements in or relating to propulsion means and has special reference to the improvement of the physical characteristics of a means of propulsion such as a rocket motor or of a selfpropelled projectile and its efliciency at low temperatures.

More especially this invention relates to improving the efficiency of such propulsion means or of a selfpropelled projectile over a wider temperature range than is at present the case.

A very serious limitation on the etficient use of many explosive materials such as are used in projectiles, e.g. rocket guided or unguided missiles, or in boost motors for use to aid aircraft in take off, is that the available efficiency of the explosive charge decreases with decreasing temperature.

In this specification the term propulsion means is used for a unit or units comprising essentially a pressure vessel or vessels together with solid or liquid pro pellent explosive material, which material is available and the said pressure vessel or vessels is or are so adapted to produce a directional thrust for propulsion.

It is an object of the present invention to improve the efiiciency, particularly the usable temperature range, of a propulsion means.

We have found that the efilciency of a self-propelled projectile particularly in respect of the range of temperature of operation may be improved by pre-heating the propellant when the projectile is to be used at low temperatures.

According to the present invention, a projectile, e.g. a self-propelled projectile, or a propulsion means as hereinbefore defined which is to be employed at a low temperature is provided with means for pre-heating the propellant to an eflicient temperature level irrespective of the ambient or external temperature.

The propellant may be pre-heated in one or more of a number of ways, for example by circulating hot gases in or near the propellant prior to its use, or by means of an electric current which may be used, e.g. to heat the casing of the projectile or of the propulsion means. Thus electricity may be used to heat a projectile casing which may be the pressure vessel itself. This method of heating is of particular value with casings of plastic material, e.g. a glass fibre reinforced plastic, where the basic casing is electrically non-conductive and electrical heating elements, such as wire windings or other electrically conductive material in continuous or powder form may be incorporated in the plastic.

Thus in the manufacture of a propulsion unit (rocket motor or boost motor from glass fibre reinforced plastic (such as is made under the trade name Micor) metal windings, calculated to give a predetermined rate of heat energy output, may be incorporated within the walls and structure of the pressure vessel or vessels or elsewhere as may be desirable.

It will be appreciated that by theme of this invention it is possible to use efliciently a self-propelled pro- Patented Dec. 22, 1959 jectile or a propulsion unit (and thus, for example, a projectile or boost motor) at substantially any ambient or external temperature, e.g. under arctic conditions or under such temperatures as may be encountered at high altitudes. Thus a war-plane flying at high altitude is enabled to effectively use a rocket projectile which may otherwise be ineifective at that altitude.

Following is a description by way of example only and with reference to the accompanying diagrammatic drawing of one method of applying the invention to the propulsion means of a self-propelled projectile.

Referring to the drawing, the propellent material is contained in a casipg ll made of glass libres impreg;

nated and-bonded withsyntheticisin and is provided witlf a venturi 1 2'of known form. The propellent material is heated electrically by means of a winding of resistance wire 13. The leads 14 and 15 of the re"- sistance wire pass through the wall of the casing 11 and into the venturi 12 and thence to the source of electric current. The Wires in the venturi art burnt through immediately after the propellant is ignited.

The lenth and thickness of the resistance wire are selected so as to provide suflicient heat input to raise the temperature of the propellant to the desired point and to maintain it at that point.

The winding 13 is covered by weglayerstoiglass fibres impregnated and bonded with synthetic resin in order to insulate the winding and to build up the wall of the container for the propellant to the necessary strength.

We claim: a

1. A jet propulsion unit comprising a pressure vessel consisting of a casing of electrically non-conductive plastic material having contained therein a propellant explosive material serving when ignited to develop a directional thrust for propulsion of said unit, and electrical means consisting of an electrical conductor constituting a continuous electrical path embedded in the plastic substantially coextensive with the longitudinal extent of the propellant material for preheating said propellant explosive material to an efficient temperature level irrespective of the ambient temperature.

2. A jet propulsion unit comprising a pressure vessel consisting of a plastic casing having contained therein a propellant explosive material serving when ignited to develop directional thrust for propulsion of said unit, and electrical means consisting of wire windings embedded in the plastic for flgrehragg said propellent explosive material to an e cient temperature level lr respective of the ambient temperature.

3. A jet propulsion unit as claimed in claim 1, wherein the casing is of glass fibre-reinforced plastic.

4. A jet propulsion unit as claimed in claim 1, wherein the electrical conductor is in powder form.

5. A jet propulsion unit comprising a pressure vessel consisting of a plastic casing having contained therein a propellant explosive material serving when ignited to develop directional thrust for propulsion of said unit, and electrical means consisting of metal windings embedded in the plastic for preheating said propellant explosive material to an eflicient temperature level irrespective of the ambient temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,736 Marick July 23, 1946 FOREIGN PATENTS 138,746 Great Britain Feb. 19, 1920 484,438 Great Britain May 5, 1938 727,307 Germany Oct. 30, 1942 590,177 Great Britain July 10, 1947 

